Vehicle body structure conventionally known from EP 1440870 A2 includes a firewall which is formed from an aluminum alloy plate and weld-connected to the vehicle body via a steel adapter.
In the vehicle body structure, left and right adapters are riveted respectively to the left and right ends of the firewall, and a lower adapter is riveted to the lower portion of the firewall.
The left and right adapters are members that form the inner panels of left and right front pillars. The left and right adapters are joined to the outer panels of the left and right front pillars by spot welding or the like, whereby the left and right ends of the firewall are attached to the left and right front pillars.
The lower adapter is also joined to a floor panel by spot welding or the like, whereby the lower portion of the firewall is attached to the floor panel. The firewall is thereby attached to the vehicle body structure. An aluminum alloy plate is used for the firewall, whereby the weight of the vehicle can be reduced.
It is necessary to increase the plate thickness of the firewall in order to endow the aluminum alloy firewall with the same rigidity as a steel firewall. If the plate thickness of the aluminum alloy firewall is increased, the degree of freedom during forming the firewall by press molding will be reduced. Consequently, using an aluminum alloy firewall makes it difficult to mold, for example, the left and right wheel housings and other curved shape areas. It is therefore necessary to shift the aluminum alloy firewall to the rear (i.e., toward the cabin) of the vehicle body in the left and right wheel housings, making it difficult to increase the size of the cabin.
The degree of freedom in forming the aluminum alloy firewall by press molding is also reduced, and it is therefore difficult to accurately press mold the firewall. Therefore, there is a need for a development of a technique whereby an aluminum alloy firewall can be manufactured even more accurately.